details to begin at any moment. >>> in washington, a visibly angeredpresidentobamavowedon wednesday this is just round one after the defeat of a bill to expand background checks on gun sales. we'll have more and what's next on the fight for new gun safety measures coming up. >>> but we begin in boston, where we're awaiting an fbi briefing in the next hour where it's expected they'll show photos of two men they're urgently seeking in the marathon bombing investigation. now, combing through video evidence, authorities are honing in on two men seen in video and still pictures including at least one who seems to have set down a black bag and dashed away just before the explosions. all this comes as the president and first lady traveled to boston to participate in an interfaith service earlier today. in a powerful speech meant to both console and offer a rallying cry, the president vowed this terrible act will be answered. >> if they sought to intimidate us to terrorize us, to shake us from those values that deval described, the values that make us who we are as americans, well, it shoul